Chain Reaction
by berrywarbler
Summary: Sebastian is the one to initiate it, but it's Blaine who convinces her. seblainchel porn because they're my new OT3.


"Don't open it now," Sebastian said with a wink, Kurt scoffing from her other side as she eyed the envelope curiously. "Wouldn't want it to offend poor Hummel's eyes."

"If there's something vulgar in here," Rachel retorted with a small smile, "I don't want it. And I'm not passing it on to Blaine for you, either."

"Honey, if I wanted Blaine to have it, I'd hand it to him myself," Sebastian replied, grinning as he moved to leave the coffee house. "I'm sure I'll hear from you later, Rachel," he yelled, her face turning bright pink as others turned to stare at her.

"Open it," Kurt pressed, but she simply shook her head, placing the file in her bag. "Come on, I want to see what's in it," he pleaded, but Rachel stood her ground.

"I'm going to go home, make sure it's nothing I should be worried about, and then shred it and hopefully after Regional's we can get rid of Sebastian for good," she told him, picking up her cup. "Now, you were telling me about the rest of your Valentine's day."

* * *

><p>She forgot about the envelope from Sebastian until her phone rang as she was getting ready for bed, her tea waiting for her on her nightstand as she answered without looking.<p>

"Hi," Blaine's voice replied once she answered, and while she was a little confused-it was after 10pm, a late night for her-she merely lay back on her bed, letting his voice sooth her as it so often did. "So, did Sebastian come to you today?"

"He did," she told him. "I completely forgot about it, actually, he handed me an envelo-"

"Don't," Blaine interrupted, his voice slightly frenzied as she paused in her movements across the room. "I mean, it's stupid, and you should probably just rid yourself of it immediately."

"Why? How do you know what's in there?" she asked, too curious not to find the thing now, pulling it out as Blaine continued.

"I, um, got one too, and it's really just best if we pretend that we never saw them," he answered, sounding slightly awkward as she eyed it warily. She didn't answer, merely placing her phone next to her on speaker phone, Blaine's voice startling her with a quiet "You're opening it, aren't you?"

"Of course I am," she replied honestly. "You made me curious," she shrugged, pulling out a sheet of paper that looked suspiciously like a letter.

"Rachel-" he said, his voice a warning as her eyes shot open in surprise as she read over the words, propositioning something she'd never in a million years have expected.

"Is this a-"

"I think so, yes."

"Blaine, what on earth did you drag me into?" she accused, scanning over _clear attraction between you two_, _fun_, _adventurous_, _one last thrill before you settle for a life of boring, dull marriage_.

"I didn't know he'd drag you into it! And he calmed down, after the whole slushie incident. I thought he'd leave me alone, and I _told _you not to open it-"

"Wait," Rachel interrupted, a small grin forming on her face. "What does your letter say?"

"That's not important, since this is something that is _never going to happen_," Blaine emphasized, her ego hurting slightly as she brushed it aside.

"If it's never going to happen, what's the harm in telling me?" she cooed, hoping the innocence laced through her tone would be enough for him to share.

"Probably the same thing yours does," Blaine offered instead, Rachel rolling her eyes as she lay back on her bed once more, hand resting on her stomach.

"That's not descriptive enough for me, Blaine Warbler," she taunted, a grin playing at her lips at his chuckle towards the old nickname. "Come on, tell me. We're friends, you can tell me."

"I don't know, this letter was pretty….graphic," he replied after a moment, Rachel's interest only piquing even more.

"Graphic?" she asked, an eyebrow raised even if he couldn't see her. "Mine wasn't graphic."

"You sound almost disappointed by that, Miss Rachel Berry," Blaine teased, and now it was her turn to let out a soft laugh in response. "Fine, how about you tell me what your letter said, and I'll tell you mine."

"Do you promise to tell me?" she asked, chewing her lip as she moved across the room to lock her door-she wasn't proud of what she had already knew she was about to do, but she felt safer knowing her dads had absolutely no way to gain entrance.

"I promise," he said, and she could hear the grin on his face even if she couldn't actually see him.

"Fine," she sighed, dramatically, eliciting another laugh from him. "Do I have to read the whole thing word for word? It's surprisingly dry, considering what it's asking of me."

"Well, Sebastian doesn't know you as well-probably didn't want anything you could take and get him in trouble with," Blaine responded.

"And he knows you well enough to know he can get away with being graphic?" Rachel questioned, more intrigued than offended, though she supposed she should have been the latter in Kurt's defense.

"Let's just say that Sebastian and I have a….complicated relationship," Blaine struggled to get out, Rachel's interest only raising. "One that-if I tell you about it, at least, you have to promise goes no further than between us two."

"Blaine," she scoffed, because she was mildly offended. "We're on the phone discussing letters propositioning us for a threesome with another boy, I wasn't planning on telling _anyone _about this."

"Good, now read your letter. Or, at least, give me an overview."

"And then I get details?" she questioned, her voice hopeful.

"Then you get details," he assured her, her mind already racing with possible scenarios.

"Okay, well, I want you to know this letter-it brings up some reasonably questionable things, things that we've never discussed before-"

"How I'm attracted to you?" Blaine asked, sounding sure of himself in a way Rachel wasn't sure why she was surprised over.

"Yes?" she replied, her voice slightly squeaky. "Yes," she started, picking up the paper once more. "According to my letter, at least, we have a palpable tension that makes everyone question Blaine's-your-sexual orientation, that while Sebastian identifies himself as gay, he has no problem envisioning himself with me, and that I should see all the pleasures life has to offer before I settle down into a life of marriage."

"Wow, he was really tame in your letter," Blaine said in surprise, Rachel practically pulling her hair out in frustration that he wouldn't get on with explaining anything to her.

"Blaine!" she said sharply, and his low chuckle-the one she hated to admit had her body reacting in a way it strictly shouldn't, her stomach swooping low and her breath hitching just a bit-didn't deter her. "Spill!"

"All right, all right," he laughed, sounding nervous. "But, just-please don't hate me, okay?"

"I could never hate you," she promised earnestly, the idea of Blaine doing anything horrible enough to ever force her affection off of him ridiculous.

"Well," he started, clearing his throat. "It's kind of a long story, but I might have started into some sort of…" he trailed off, Rachel's brain landing on a conclusion she wasn't sure about.

"Are you sleeping with Sebastian?" she asked, her voice barely above a breath as he cleared his throat uncomfortably again before answering with a quiet 'yes'. She didn't know how she felt, because her first reaction was disgust-how he could do this to Kurt, with someone who had hurt him as badly as he had. But then she was curious again, more curious than she had ever been about his relationship with Kurt, because Kurt was her best friend. But Sebastian was different, new, someone she could allow herself to picture with Blaine. "Why?" was the question she finally settled on, and it seemed to startle Blaine on the other end.

"It just kind of…happened," he finally replied. "We started talking, and one night he was asking me about Kurt, and then he started asking me about my sex life with Kurt, and-"

"And you gave explicit details on your sex life with your boyfriend to a boy who is basically stalking you?" Rachel supplied helpfully, Blaine's laughter loud on the other end.

"Pretty much. I mean-wow, this is bordering on far too much information now-"

"I think we've pushed past that point, Blaine," she shrugged on her end, a mischievous grin on her face. "Did you two have phone sex?"

"Rachel!" Blaine squealed, his voice high pitched and she didn't fight off the laugh that erupted from her own body.

"And that somehow turned into real sex?"

"And that somehow turned into real sex," he finally agreed, his voice quiet again. "And then he-god, I don't even know how he figured it out-he saw us, I suppose, at the Lima Bean one day. And he said that I don't look at any other girl the way I look at you, and I tried to point out that you're probably the closest girl friend I have," he continued, her heart warming at the sentiment, "but he pressed on and on until I admitted that yes, we had a brief fling last year, and yes, I was still attracted to you, even if I lied about it. Sorry about that, by the way."

"It's probably for the best anyways," Rachel replied, her voice distant as she wrapped her mind around the fact that Blaine Anderson, the boy every girl secretly wanted because of his charming personality, dashing good looks and incredible talent, was attracted to her. "So he proposed a threesome? In a letter form?"

"Well, the idea might not have been entirely his."

"What do you mean?" Rachel asked curiously, her throat drying at the idea that Blaine had been behind this all along.

"I never meant to initiate anything-the last thing I wanted was to drag you into all this, Rach-but I might have said some things, and they might have spurred him into doing this," Blaine divulged, Rachel's grin only growing more as her skin flushed, her mind wandering with images of what Blaine might have told him.

"What kind of things?" she asked, her voice low as she licked her lips, wondering if he'd actually tell her, before she remembered the letter he had yet to read to her.

"Rach-"

"You never read me your letter," she added, her fingers skimming the skin above her shorts, eyes open wide as they stared at the ceiling above her.

"You're sure about this?" he asked, and she could only hum in agreement as he let out another sigh, though she had noticed that his own voice had dropped down an octave as he began speaking. "'Blaine'," he started, and her fingers dug into her own hip momentarily as she waited, her breath still. "'I want you to know that I've been seriously considering what you said the other night, about how if we were to invite a third person in, it wouldn't be Kurt you wanted with us-how it would be Rachel Berry. Now, as you know, my first objection was that she's obnoxiously loud, and oddly enough that may be what turned me onto the idea myself.'"

"I am not obnoxiously loud!" Rachel argued, snapped out of her reverie for a moment before Blaine lulled her back in.

"I'm sorry, Rach, but you are. Now, do you want me to continue, or not?"

"Please do," she breathed, and she could practically hear him gulp on the other side of the phone, her lip between her teeth.

"Okay then," he said quietly, seeming to try and focus his attention once more. "'To be frank, Blaine, I think I'd enjoy nothing more than watching the two of you together, or of having a piece of her myself. Girls are very rarely my type, but ones as demanding and passionate as she is are certainly a great addition in the bedroom. The image of her between the two of us-well, you can only imagine how difficult it would be to continue writing this letter if I went on down that path,'" Blaine spoke, his own voice slightly hoarse as he read to her, the images Sebastian had laid in front of them tantalizing the forefront of her brain.

"Oh," was all she could say, her voice slightly high pitched, her fingers still pinching lightly at her skin as if it would stop the desire that had started coursing through her body, pause her from crossing a line she didn't think they'd come back from.

"'But now that I've started, I might as well continue, and what better way to start than with her laying on my bed, spread apart and eager for us. Her hands being put to good use as she strokes me, her mouth working on you as I slide into her easily,'" Blaine continued, and she was sure she caught his own breath hitch as he read the words that only seemed to spur her own fingers on. Her mouth felt empty, hollow, as if it was missing something, the mental image of Blaine's cock sliding in and out of it easily accessible as she pushed aside her underwear, her own fingers teasing her clit momentarily with a small gasp before she moved lower.

"'I'd make her hum around you, Blaine, push her into a withering mess until you came into her, her pretty pink tongue darting out as she cleaned the two of you up-'" She could picture it, too, all in her head, the look of pleasure on Blaine's face as she wiped her mouth clean of his come, Sebastian's fingers inside of her instead of her own.

"Then what?" she found herself asking, unable to stop herself from letting out a small moan.

"Are you-Rachel, are you touching yourself right now?" Blaine asked, sounding slightly incredulous but mostly turned on, his voice low and gravely and she couldn't do anything but let out a breathy 'yes' before he growled in response, only serving to push her fingers deeper inside herself, angling to find the precious spot that was sure to make her come sooner rather than later.

"You stopped," she pouted, swiping her thumb over her clit and letting her body shudder silently as he made some sort of low groan from the back of his throat, and suddenly she was hit with the mental image of Blaine in his bed, stroking himself while he thought about her in her own bed, playing with herself. "Blaine, are you-"

"God, yes," he let out, his breathing irregular and it was this more than anything that pushed her over the edge, her teeth digging into her bottom lip as her eyes rolled back and she tried to come as quietly as possible, not wanting to get caught-especially not while on the phone with Blaine, of all people.

"You want me to do all those things?" she asked after a moment, her chest still heaving as she grabbed a tissue to wipe her fingers off on. "You want me to-to suck your cock, to fuck you while Sebastian watches?"

"Yes," Blaine whined, his own voice a higher pitched than it was a second ago, a warm grin on her face.

"Maybe I could suck Sebastian off," she continued, her voice quiet, "feel him come inside my mouth while you're the one fucking me," she went on, Blaine's quiet whine all she could focus on, her body flushing even more with the desire to go again-but this was about him now, about getting him off. "You could have me, you know. Any way you wanted me. Because, god, Blaine, I want you so bad," she cooed, and she would have felt embarrassed saying these things aloud to anyone else, but Blaine was whispering her name in a way that had her closing her eyes and imagining his body pressed firm against her own, his mouth on her neck, her breasts, between her thighs as he brushed against her lightly.

She whispered these things to him, going into far more explicit details than she would have with Finn, only to be rewarded after a moment with Blaine's final cry, a little louder than the rest as he called out her name, a proud smirk on her features as her fingers idly traced over her body in an attempt to cool it down. "You know, if you really want this to happen," she said after a moment, "I think that should be arranged."

"Rachel, we shouldn't-"

"Says the boy cheating on his boyfriend already," she scoffed. "We've already crossed a line, Blaine. If we're going to do this, then we're going to do this all the way."

"So you're in?" he asked, his voice helpful and only reassuring her of her answer.

"Count me in."

* * *

><p>It took another two weeks before they could actually all meet up, their schedules busy and conflicting, though Rachel and Blaine's phone calls became a more regular thing, her desire for him growing every time they came from opposite sides of the phone line, their voices hush and quiet as they talked. It was harder to keep their growing affections down in public, when Rachel couldn't go up to him before class and kiss him, couldn't feel his body pressed against her own after school. Finn complained, one afternoon, that he felt like she was losing interest in him, and she was. She just didn't know how to break the fact to him without breaking his heart and her own in the process.<p>

Still, the Saturday they all planned together-at Sebastian's house, where no one they knew would think to look for them, Finn convinced she was ill with a cold and Kurt told Blaine had to go out of town to visit his brother for the night-seemed too far away for her, and she knocked on the door with a quick hand when she finally arrived.

It was Sebastian who answered the door, grinning-or, more appropriately, leering-at her as she cleared her throat, Blaine coming to her rescue a moment later. "You came," he grinned, and she could only smile in response.

"I told you I would," she responded, letting Sebastian pull her into the house. "I never back down from a promise."

The boys just tittered, Sebastian slinging his arm easily around her waist as he led her up a flight of stairs, Blaine trailing carefully behind them. "Now, Blaine tells me the two of you have spent the past couple weeks becoming more comfortable with one another," Sebastian started, Rachel's cheeks flushing red despite herself and the situation she was knowingly walking into. "Which, quite frankly, was a long time overdue apparently. Now, I want you to be comfortable-this is as much for you as it is for us, after all," he smirked, pushing open a door to a grand room, the inviting bed located in the center of it as he led her to it, Blaine leaning against a post on the frame. "So if this gets to be too much, or you want to stop, you have to tell us."

"Rachel wouldn't let you do anything she doesn't want to," Blaine said with a confidence she had to admire, a smile on her face as she slipped onto the bed with ease. Sebastian sat next to her, his long fingers tracing over her bare thigh-she had decided on a simple dress, knowing it wouldn't stay on her body too long anyways-making her skin squirm as she looked up at Blaine.

"I'll be sure to speak up if I feel uncomfortable," she assured Sebastian, though he seemed less interested in her words now as his hand moved higher, moving the hem of her dress upwards until it was barely covering anything at all.

"Good," he responded a moment later after he seemed to be finished examining her skin there, his lips catching her own rather suddenly in a kiss. His lips were hard against her own, hand holding her head in place as he nipped at her bottom lip and causing her own to fall apart, allowing his tongue access to the inside of her mouth. She'd rarely had a kiss so ferocious before, the only feeling behind it a desire and want that she had to admit was intoxicating to her. He wanted nothing more than her body, and while she knew she should have been turned off at the prospect, it only made her own tongue glide across his.

When Sebastian finally left her lips to focus on her neck, sucking and biting down harshly, she turned her head to find Blaine staring at them, still leaning against the frame of the bed, arms crossed over his chest.

She motioned for him to move closer to them, rolling her eyes as he merely smirked at her before Sebastian hit a sensitive spot near the base of her neck, causing her eyes to flutter closed momentarily as her body tensed. Sebastian let out a low chuckle, smoothing over the spot he had bitten with his tongue. "Your girlfriend's first weak spot," Sebastian chuckled, and Rachel wanted to argue the girlfriend statement, but Blaine was finally moving closer to them, moving past her and next to Sebastian. She wanted to whine and protest, but the idea of the two of them intrigued her, and as Sebastian pulled away from her to attach his mouth to Blaine's, she kept her comment to herself.

She watched avidly, licking her lips as Blaine moved his hand across Sebastian's body to Rachel's own, his fingers warming her skin in a way that Sebastian, and even Finn, wasn't capable of. His eyes met her own as Sebastian continued assaulting his mouth, grinning before he pulled away from the boy and pulled her own face towards him, their lips crashing eagerly.

She wanted to melt into him, memorizing the way his lips felt as they glided on top of her own, Sebastian moving from between them to behind Rachel, pushing her forward and onto Blaine's lap with little resistance from either of them. Her hips straddled his own as her fingers pulled gently at the hair on the nape of his neck, Sebastian moving behind her and moving both his and Blaine's hands up her body.

She moaned lightly into Blaine's mouth as his teeth pulled onto her bottom lip, Sebastian unzipping her dress without a question, Blaine's hands moving up her thighs once more. She squirmed lightly at their touches, as Blaine lifted the fabric of her dress over her head, leaving her in only her bra and panties as Sebastian pressed his body against her back, sending a shiver through her as she realized it was his bare torso touching her own skin. "Undress him," Sebastian husked in her ear, and she didn't have to be told twice as she moved Blaine out of his sweater, throwing it off the bed without a second thought as his mouth attached itself to her collarbone, working its way down her skin.

"You can do better than that, Berry," Sebastian growled, and she turned her head to glare at him, noting the dark coloring of his eyes as he pulled her off of Blaine, kissing her deeply once more and eliciting a small squeak out of her mouth as she found herself turning around, trying to take more of Sebastian into her skin as his fingers moved to unhook her bra, forgetting about Blaine completely for a moment as his mouth suctioned its way onto her breast, sucking her nipple into his mouth and swirling his tongue around it as his hands gripped onto her hips to hold her tight.

She let herself get lost in the sensation for a moment before she felt Blaine's hands return to her waist, his fingers playing with the hem of her underwear before pushing it off her completely, leaving her completely naked and completely without shame as Sebastian sucked at the skin on her hip, his eyes hungry as his tongue slid over her flushed skin.

She noted as Blaine moved his hand down Sebastian's skin, noted how his skin practically jumped under Blaine's caresses, and she found herself momentarily envious of the sensation before Sebastian was pushing her backwards onto the bed, his teeth marring the inside of her thigh as Blaine continued his descent down Sebastian's body, her breath becoming more shallow as she watched his hand wrap itself around Sebastian's cock at the same time Sebastian parted her own skin, his tongue lapping at her without warning.

"Oh!" she exclaimed, trying to keep her head up to watch Blaine's hand, to watch what the other boys were doing but she couldn't focus on anything besides how Sebastian's tongue was working its way around her clit, working its way inside her teasingly, leaving her gasping for more. She was vaguely aware of Blaine's chuckle as she gave up, legs opening wider for Sebastian to have more access to her, her hips moving of their own accord in their pleas for more.

Sebastian lifted his head momentarily, only to rest it on her thigh as he let out a small groan, Blaine smirking as she lifted her head to examine why Sebastian's fingers had replaced his tongue. She noticed a glare, the words "Fuck, Blaine, she tastes amazing," falling from Sebastian's mouth before Blaine leaned over to kiss him, sucking Sebastian's tongue into his mouth in an attempt to get the taste of Rachel into his own, the image enough to send Rachel spiraling into an orgasm, her body clenching tightly around Sebastian's fingers as she let out a loud cry.

He pulled out of her, the boys moving around and before she realized what was going on, Blaine was hovering over her, his lips attached to her own. She didn't complain, instead pushing him until she was on top of him, her hips once more locked around his own. He grinded into her for friction, which Rachel was more than ready to give in return, and it took her a moment to realize Sebastian was there next to her, moving between the two of them and moving her hips to the perfect location so she could slide onto Blaine with ease.

She did so without a second thought, desperate and needy for anything she could get, her hand shooting out and grabbing onto Sebastian's arm as Blaine gripped onto her thighs tightly, his eyes closed as he waited for her to make the next move. "Jesus," he whispered, breathing heavily before she started moving, lifting her hips up slowly only to slide back down, moving almost tantalizingly slow as she licked her lips and motioned for Sebastian to come nearer to her.

"Didn't forget you," she promised, and Sebastian merely let his head fall to her shoulder as she managed to come up with some sort of rhythm, moving herself on top of Blaine and stroking Sebastian quickly, her fingers sticky with the precum that was leaking heavily from him.

"Didn't think you did, pretty girl," Sebastian murmured, his voice hoarse as he let his own hand trail down to her clit, the sensations overpowering her as she felt herself rapidly approach another orgasm, her hands falling forward onto Blaine's chest as he pushed into her a few more times, his hips jutting harshly into her own before he let himself release into her, his groans mingling with her own. She felt slightly bad as Sebastian had to finish on his own, her body worn out as she collapsed, her eyes barely staying open as she felt Sebastian pull her off of Blaine a moment or two later, a small whine emitting from her mouth.

She reached for Blaine as soon as she was placed next to him on the bed, her arms wrapping around him as Sebastian sighed heavily, Blaine grinning at Rachel before placing a small kiss on her forehead, his own hand resting easily on her hip. "You're going to be a sleeper like Blaine, aren't you?" Sebastian complained from behind them, and she merely nodded as she burrowed in closer to Blaine.

"Sleep," Blaine murmured, his eyes leaving Rachel's face momentarily to glance at the other boy, and while she could hear him put up a fuss about it, it was only a moment later that he was pressed against her, his own arms wrapped around her and resting on Blaine's side. She hummed contently, comfortable in her place between them, before letting herself drift off into a peaceful sleep.


End file.
